1. Field of the Invention
The present invention relates to a zoom lens suitable for an image capturing optical system of image pickup apparatuses such as digital still cameras, video cameras, TV cameras and monitoring cameras.
2. Description of the Related Art
As an image capturing optical system used for image pickup apparatuses, a zoom lens having a wide angle of view, small distortion and high resolution is required. As a zoom lens having a wide angle of view, a negative lead zoom lens is known in which a most-object side lens unit (first lens unit) has a negative refractive power.
In order to increase the angle of view of the negative lead zoom lens and improve the resolution thereof, it is necessary to, for example, increase the negative refractive power of the first lens unit. In this case, since a large barrel-shaped distortion is generated, a large-diameter aspheric lens is generally used as the first lens unit having the negative refractive power to correct the distortion while increasing the angle of view.
In order to suppress generation of distortion due to increase of the angle of view and thereby to achieve a good optical performance, it is important to appropriately set a lens configuration of each lens unit constituting the zoom lens, a refractive power of each lens unit, a zoom type and the like. For example, in order to suppress the generation of distortion by using an aspheric lens, it is important to appropriately set a position of an aspheric surface in an optical system, a lens surface shape to which the aspheric surface is applied, an aspheric amount and the like. When such settings are inappropriate, it is difficult to achieve a high optical performance while miniaturizing the entire zoom lens and increasing the angle of view.
Japanese Patent Laid-Open No. 2005-106878 discloses a wide view angle zoom lens including a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a negative refractive power, which has a total angle of view of 120° at a wide-angle end and a zoom ratio of approximately 2.
In this zoom lens, even though two aspheric lenses are used in the first lens unit having the negative refractive power, relatively large astigmatism and coma aberration are generated.
Japanese Patent Laid-Open No. 2008-046208 discloses a wide view angle zoom lens including a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having negative refractive power and a fourth lens unit having a positive refractive power, which has a total angle of view of 106° at a wide-angle end and a zoom ratio of approximately 2.1.
In the zoom lens, although two aspheric lenses are used in the first lens unit having the negative refractive power, distortion is not sufficiently corrected.
Japanese Patent Laid-Open No. 2008-233284 discloses a wide view angle zoom lens including a first lens unit having a negative refractive power and a second lens unit having a positive refractive power, which has a total angle of view of 113° at a wide-angle end and a zoom ratio of approximately 1.7.
In this zoom lens, although two aspheric lenses are used in the first lens unit having the negative refractive power, distortion is not sufficiently corrected, and the entire zoom lens is large in size relative to the total angle of view and the zoom ratio.
US2011/0109974 discloses a single focus lens having a total angle of view of approximately 127°.